The invention relates to a device for short-circuiting a first electrical line with a second electrical line, it being possible for the first electrical line and the second electrical line to be short-circuited by a mechanical switching device.
Such short-circuiting devices are known e.g. from Siemens product information xe2x80x9cShort-circuiter SITRAS(copyright)SCD96 voltage limiting device for DC railroad installationsxe2x80x9d, Order No. A52811-C2720-D11-A5-00B1. The known short-circuiting devices are used in railroad power supply installations. In the case of a DC supply, the first electrical line is in this case formed by the return line (which is the rail in DC railroad installations) and the second electrical line is formed by the grounding line.
In the event of insulator flashovers, in the event of flashovers on horn arresters of the overhead-contact line installation and in the event of other undesired connections between the overhead-contact wire voltage of, for example, 1500 volts DC voltage and grounded installation components, voltages of up to a maximum of 1500 volts occur between the rails, which form the return lines, and the grounding installation. This means that, firstly, impermissible contact voltages can occur on the return line. Secondly, assemblies which are connected to the rails and whose withstand voltage is insufficient can be destroyed. If the arcs are not extinguished owing to the grid follow currents or the short circuits persist for other reasons, the electromechanical switching device of the short-circuiter intervenes after a response time of 60 milliseconds, for example, and connects return line and grounding installation. The section protection triggers in the event of faults of high current intensity.
EP-B 0 806 071 discloses a short-circuiting device in which a first electrical line can be short-circuited with a second electrical line by means of an electromechanical short-circuiting bridge which is driven in a complicated manner.
Swiss patent 1,307,822 describes a short-circuiting device in which a first electrical line can be short-circuited with a second electrical line by electronic means. This device also requires comparatively complex driving.
It is an object of the present invention to provide a short-circuiting device which is constructed in a simple manner and has short response times.
The object is achieved according to the invention by means of the features of claim 1. Further claims respectively relate to advantageous refinements of the invention.
The invention""s device for short-circuiting a first electrical line with a second electrical line has a mechanical switching device by means of which the first electrical line and the second electrical line can be short-circuited. According to the invention, at least one first electronic switching device is arranged in parallel with the mechanical switching device and at least one second electronic switching device is arranged reverse-connected in parallel with the first electronic switching device, in which case a voltage difference that occurs between the first electrical line and the second electrical line can be bridged by at least one of the electronic switching devices. The first electronic switching device switches if the potential of the second electrical line is greater than the potential of the first electrical line by a predeterminable difference value, and the second electronic switching device switches if the potential of the first electrical line is greater than the potential of the second electrical line by a predeterminable difference value.
The device according to claim 1 thus has a mechanical switching unit and an electronic switching unit, which, in terms of their function, are each independent of one another. The mechanical switching unit comprises at least one mechanical switching device and the electronic switching unit is formed by at least one first electronic switching device and also by at least one second electronic switching device. The two switching units are each driven by at least one dedicated independent drive arrangement and, consequently, short-circuit the first electrical line and the second electrical line independently of one another. The drive arrangement of the electronic switching unit, i.e. the drive arrangement of the first electronic switching device and of the second electronic switching device, does not require an auxiliary voltage. If one switching unit fails or the auxiliary voltage fails, the short-circuiting function is thus still ensuredxe2x80x94at least at high voltagesxe2x80x94by the other switching unit. Optimum protection of people is thus ensured by virtue of the redundancy of the device in accordance with claim 1.
By virtue of at least one first electronic switching device and at least one second electronic switching device, the short-circuiting device defined in claim 1 has a significantly shorter response time. Furthermore, the response behavior of the device according to the invention is independent of the sign of the voltage difference that occurs between the first electrical line and the second electrical line. This improves the protection of people against electric shock and the protection of electronic assemblies connected between rails and grounding installation in the case of railroad power supply installations, since overvoltages between the first electrical line (return line, formed by the rail) and the second electrical line (grounding line) do not occur, or only occur briefly. As a result, damage to the electronic assemblies between rails and grounding installation can be avoided with high probability.
In accordance with a refinement according to claim 2, after the bridging of the first electrical line and of the second electrical line by at least one of the electronic switching devices, the mechanical switching device is additionally triggered by the latter. As a result, in an advantageous manner, the bridging electronic switching device is loaded by the high short-circuit current only for a very short time, since, after the response of the mechanical switching device, the short-circuit current flows exclusively via the mechanical switching device, which can withstand higher current loading.
Within the context of the invention, the power semiconductors in the electronic switching devices may be designed for example as GTO thyristors, as thyristors or as transistors.
In embodiments in accordance with claims 4 and 5, the electronic switching devices are designed as thyristor circuits.
In the embodiment according to claim 4, the thyristor circuit comprises at least one thyristor, whose cathode is connected to the first electrical line and whose anode is connected to the second electrical line. A drive circuit comprising a series circuit formed by breakover diode, triggering series resistor and protection diode is connected to the gate of the thyristor.
In the embodiment according to claim 5, the thyristor circuit comprises at least one thyristor, whose cathode is connected to the second electrical line and whose anode is connected to the first electrical line. A drive circuit comprising a series circuit formed by breakover diode, triggering series resistor and protection diode is connected to the gate of the thyristor.
In accordance with a refinement according to claim 6, a current detecting device is additionally connected upstream of the thyristor, which device drives the mechanical switch. After the closing of the mechanical switching device, the thyristor turns off automatically on account of its being arranged in parallel with the mechanical switching device. By contrast, a GTO thyristor can additionally be forcibly turned off. The device in accordance with claim 6 affords further improved protection against overvoltage damage for the electronic assemblies.